Many military vehicles in use today employ the M36 or DIM36 weapon sight. These periscope-type sighting systems typically use mirrors and/or prisms to reflect light at approximately 45 degree angles to the axis of the objective lens set used in the device. The limitation of all prior art day night sighting systems, including periscope-type sighting systems, is that a separate objective lens set is used for each camera, one for day and one for night time viewing, and therefore, of necessity, are looking at different images of the same or similar field of view (FOV). To enhance these images, fusion means are employed in the prior art, but fusion also suffers from the same inefficient use of merging two different images of the same FOV.
Sighting systems can vary greatly depending on the application and origin of design. In cases where the requirements are for multiple detection schemes, such as day versus night, designs become more complicated in order to make the system perform properly while viewing each scheme. In some cases fusion is a requirement such that at least two views can be overlaid in order to get an image while looking at both detection schemes at the same time. Care must be taken such that the content of the images to be fused is close enough to being identical in content so that once fused, the extent of one image matches up with the extent of the other such that there is a good image. If the two images being fused can be created from the same bundle of light, the content is the same and fusion can occur, including variables such as perspective, field of view, and magnification. Once detected, electronic methods can get the images lined up and overlaid properly. But, if the incoming images do not carry the same content, not only can fusion not occur properly, but the user of the system may be able to detect differences in the image being displayed. For example, if there is an offset in one image relative to the other, something that is visible on a viewing monitor of the day may shift far enough such that it is not visible in the field of view of the night image being displayed. If this occurs, the user will obviously not be able to compare both images and hope to identify the object using both detection schemes.
What is needed is a Multiple Spectral Single Image Sighting System Using A Single Objective Lens Set and method that exploits the simultaneous capture of just enough high intensity light to enable an image to be reflected onto a day camera and maximizing the amount of remaining low intensity light to reflect the same image onto a night camera using a single objective lens set, instead of two, within an objective assembly housing. The method of the invention discloses the optimization of the limited diametrical space of the housing to maximize the amount of light available for low light conditions, so that the same image from two or more spectral bands can be transmitted each camera system to a video display monitor. Enhanced fusion of the same image, rather than from two distinct images is now possible. One way to achieve this is to ensure that the bundle of light that is being detected remains coaxial with respect to its objective lens set throughout its optical path until it gets to its detection surface. Many of the embodiments of this present invention, if not all, achieve this coaxial aligning so as to create and redirect duplicate images.